| 摘要 |
A protected/security document is provided that foils counterfeiting even if a laser photocopy machine (such as a Canon 500 color copier) is utilized. The document has at least three discrete half-tone printed bands disposed on its surface, provided by dots or lines. Each printed band has a different screen density and within each bands the dots or lines comprise a warning word or symbol (e.g. "Void"), or a background. The dots or lines of either the "Void" or background drop out when photocopied, while the dots or lines of the other do not. The dots or lines that do not drop out may be dimensioned so that there are about 24-34 per centimeter, while for those that do drop out there are about 52-64 per centimeter. The bands are typically arranged either linearly or in concentric circles, and interband areas having density gradually transitioning between the densities of adjacent bands are provided. The total density variation between discrete bands is typically about 10-35%, depending upon ink color, typically about 1.0-10% gradation between adjacent bands. Full tone indicia, which does readily reproduce, is also printed on the substrate.
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